WASHINGTON - Congress may weigh in on a rule governing the detention of migrant children.

The so-called Flores Settlement Agreement limits the time children may be held in immigration detention to 20 days. Flores has gotten in the way of Trump administration plans to detain families together as a unit after they cross the U.S.-Mexico border illegally.

Earlier in September, the administration issued a proposed rule that would allow migrant children to be held longer than 20 days along with adult family members.

But as Republican Sen. Ron Johnson of Wisconsin pointed out Tuesday at a hearing of the Senate Homeland Security and Governmental Affairs Committee, the courts are not likely to let the proposed rule change stand.

"It's going to be a high probability. The courts will intervene, and this rule-making will never be put into effect," Johnson said.

The rule is currently in a public comment period.

Without congressional intervention, the agencies enforcing immigration policy are in a bind. They have only two options when family units enter the country illegally.

"And both of them are bad," Johnson said. "We either have to enforce the law, and then we're forced to separate parents from children, and nobody wants that to happen, OK? That's no longer the policy. Or revert to the Obama-era policy - which is what we're under right now - which is when we apprehend these families, we can't hold them, we can't really determine parentage, and we release them into the interior."

FILE - A member of the Central American migrant caravan, holding a child, looks through the border wall toward a group of people gathered on the U.S. side, as he stands on the beach where the border wall ends in the ocean, in Tijuana, Mexico, April 29, 2018.

Inefficient system

The House of Representatives' Appropriations Committee approved a budget amendment in June that would overrule Flores and permit children to be detained indefinitely.

But Democratic senators on Tuesday were heated in their opposition to detaining children at all.

Citing the high costs of building additional detention facilities and keeping people in them, Democratic Sen. Claire McCaskill of Missouri called for increasing the efficiency of the immigration system which can keep people on hold for years before their cases get through the immigration courts.

"Our system on asylum determination and removal couldn't be more inefficient," McCaskill said. "We should be starting with a bill that requires electronic records! Do you know, if they have to do a hearing in Texas and the file is in California, they have to FedEx the file? No system in this country is still all-paper. No system in this country is still all-paper except this one!"

The immigration courts currently have a backlog of almost 800,000 cases.

Children's mental health

To other Democratic senators, the issue is one of children's physical and mental health.

"What this hearing comes down to for me is whether the federal government should be keeping children in detention indefinitely while waiting for a judge to review their case. That's frankly not who we are as a country," declared Democratic Sen. Maggie Hassan of New Hampshire.

FILE - Children form a line as undocumented immigrant families are released from detention at a bus depot in McAllen, Texas, June 22, 2018.

The number of children held in detention grew to 12,800 in September. Most are unaccompanied minors, but 419 are children who were separated from their families and have yet to be reunited.

Members of the panel of four government witnesses at the hearing pointed out that under the current system, disparity exists between single adults who illegally cross the border and families. The adults are put in detention; the families are released.

And according to Acting Deputy Assistant Attorney General Joseph Edlow, there is a big difference in the length of time to adjudicate cases. The immigration status of those in detention is about 40 days. For those not in detention, it's 752 days.

"The modification of the Flores Agreement is more so a deterrence ... by creating the legal framework that does not create disparity in the treatment of single adults and or family units," said Robert Perez, acting deputy commissioner of Customs and Border Protection.

Edlow indicated the federal government will stick up for its proposed rule. "The department will stand ready to defend the challenges as they come forward," he told the senators.

To Johnson, the situation is an opportunity for Congress to act "and pass a law and fix this particular problem."